diff --git a/R/mediate.R b/R/mediate.R
index 808feb741..daaef2d29 100644
--- a/R/mediate.R
+++ b/R/mediate.R
@@ -17,7 +17,7 @@
 #'   as mediator in the model. (Default: \code{NULL})
 #'
 #' @param assay.type \code{Character scalar}. Specifies the assay used for
-#'   feature-wise mediation analysis. (Default: \code{"counts"})
+#'   feature-wise mediation analysis. (Default: \code{NULL})
 #' 
 #' @param dimred \code{Character scalar}. Indicates the reduced dimension
 #'   result in \code{reducedDims(object)} for component-wise mediation analysis.
@@ -174,10 +174,9 @@ setMethod("addMediation", signature = c(x = "SummarizedExperiment"),
 #' @importFrom SingleCellExperiment reducedDim reducedDimNames
 setMethod("getMediation", signature = c(x = "SummarizedExperiment"),
         function(x, outcome, treatment,
-            mediator = NULL, assay.type = "counts", dimred = NULL,
+            mediator = NULL, assay.type = NULL, dimred = NULL,
             family = gaussian(), covariates = NULL, p.adj.method = "holm",
             add.metadata = FALSE, verbose = TRUE, ...) {
-
         ###################### Input check ########################
         if( !outcome %in% names(colData(x)) ){
             stop(outcome, " not found in colData(x).", call. = FALSE)
diff --git a/man/getMediation.Rd b/man/getMediation.Rd
index f46a3b15d..ad2ff1269 100644
--- a/man/getMediation.Rd
+++ b/man/getMediation.Rd
@@ -32,7 +32,7 @@ getMediation(x, ...)
   outcome,
   treatment,
   mediator = NULL,
-  assay.type = "counts",
+  assay.type = NULL,
   dimred = NULL,
   family = gaussian(),
   covariates = NULL,
@@ -62,7 +62,7 @@ used as treatment in the model.}
 as mediator in the model. (Default: \code{NULL})}
 
 \item{assay.type}{\code{Character scalar}. Specifies the assay used for
-feature-wise mediation analysis. (Default: \code{"counts"})}
+feature-wise mediation analysis. (Default: \code{NULL})}
 
 \item{dimred}{\code{Character scalar}. Indicates the reduced dimension
 result in \code{reducedDims(object)} for component-wise mediation analysis.